National Summary Data, Antibiotic Resistance

The answer to antibiotic resistance and swine health may be waiting on your spice rack.

Researchers are studying how oil from common herbs like oregano, thyme and nutmeg could boost the health of young pigs and reduce reliance on antibiotics.

All animals carry bacteria in their intestines.

Giving antibiotics to animals will kill many bacteria, however, when animals are given antibiotics for growth promotion or increased feed efficiency, bacteria are exposed to low doses of these drugs over a long period of time. This type of exposure to antibiotics resistant bacteria, according to the Centers for Disease Control and Prevention.

Recognizing that the use of antibiotics in food animals may lead to broader public health consequences, the U.S. Food and Drug Administration placed restrictions on antibiotic use in animals in 2016. Health Canada banned the use of antibiotics in animal diets the following year.

Antibiotic growth promoters have been widely used in pig diets, especially in nursery diets, to control incidences of post-weaning diarrhea and to improve growth performance. This widely used practice could lead to the spread of antimicrobial-resistant bacterial pathogens in both pigs and humans, posing a significant threat.

Bacteria such as Salmonella and E. coli can be transmitted from animals to humans through food, by direct contact with animals or through contaminated water.

Scientists at the University of Manitoba in Winnipeg, Canada, and the Shanghai Lab-Animal Research Center in Shanghai, China, have conducted a study to determine if essential oils can be an effective alternative to antibiotics for pigs.

Essential oils are natural bioactive compounds derived from plants and have positive effects on animal growth and health. They have been widely used as traditional medicines to improve health and cure diseases in humans.

The five essential oils tested in the Canada-China study were: carvacrol, which mainly comes from oregano; thymol from thyme; citral from lemon myrtle or lemon grass; eugenol from clove oil, nutmeg or basil; and cinnamaldehyde from cinnamon bark.

The effects of essential oils on inflammation, oxidative stress and other ailments led to better production performance, according to an abstract for the study. Essential oils have good potential as antibiotic alternatives in feeds for swine production, according to Faith Omonijo, the study’s lead research assistant at the University of Manitoba.

There are numerous studies demonstrating that essential oils have several properties, such as antimicrobial, antioxidative and anti-inflammatory effects, feed palatability enhancement and improvement in gut growth and health, she said.

“In general, I would say that research into essential oils as antimicrobial alternatives (for swine) has had mixed results,” said Dr. Harry Snelson, executive director of the American Association of Swine Veterinarians. “Some studies seem to show potential under certain circumstances and for specific disease challenges.”

With the exception of citral, all of the essential oils tested were shown to be effective against E. coli, Salmonella typhimurium and Brachyspira hyodysenteriae; all lead to diarrhea, while Salmonella typhimurium can contribute to erysipelas. Eugenol and thymol were both effective against Pseudomonas which can lead to melioidosis.

Eugenol was also listed as being effective against both Salmonella typhimurium and Salmonella anatum, which can lead to enteritis – an intestinal infection marked by watery diarrhea, abdominal cramps and sometimes fever.

“Obviously, these products must be efficacious, but, in addition, the inclusion of these products in swine diets must be economical, palatable and promote feed intake and efficiency,” Dr. Snelson said.

Essentially – they have to be cost effective, and pigs have to like them.

“That’s a fairly high bar, but new technologies may facilitate the achievement of these objectives,” he said.

The Canadian and Chinese researchers admit that the minimal amount of essential oils needed to kill pathogens may not ensure the optimal feed intake, and the cost may be too high in swine production.

Another benefit to using essential oils versus antibiotics, is withdrawal. Certain feed additives must be withdrawn from the feed before slaughter to ensure residue-free carcasses. This would not necessarily be the case with all-natural essential oils. This would depend on federal and state laws and regulations.

The distribution of all animal feeds entering interstate commerce is regulated by the Food and Drug Administration (FDA). In addition, the FDA monitors the amounts of drugs or feed additives used in the manufacturing of medicated feeds. There may also be specific state laws governing distribution of feeds and the production of medicated feeds.

“Swine veterinarians and producers are always looking for effective disease treatment and control technologies,” Snelson said. “We would certainly consider any technologies that improve animal and public health and swine well-being.”

Jon Burleson can be reached at

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